CN103438832A - Three-dimensional image measuring method based on line-structured light - Google Patents

Abstract

The invention relates to a three-dimensional image measuring method based on line-structured light. The method can fast acquire three-dimensional data on the surface of an object based on the principle of the line-structured light, and can simultaneously acquire the precise edge contour data of a space object. Meanwhile, the method is simple in procedure, and in the respect of hardware, only an annular LED light source needs to be added to an existing three-dimensional image measurement instrument to achieve the method.

Description

3-dimensional image measuring method based on line-structured light

Technical field

The present invention relates to a kind of, especially a kind of 3-dimensional image measuring method based on line-structured light.

Background technology

In prior art, structured-light sensor is applied widely in reverse-engineering and field of quality control.This structured-light sensor is compared and has greatly been improved measuring speed with traditional three coordinate measuring machine contact type measurement.This class gauge head normally is comprised of a generating laser and one or two charge-coupled image sensor (Charge Coupled Device is called for short CCD) video camera.Wherein generating laser sends a laser rays, projects body surface; Ccd video camera can receive diffusing on testee.Pixel coordinate on the ccd video camera image planes can be converted into to the two-dimensional coordinate in optical plane by this system being demarcated just.Just can realize the three-dimensional scanning measurement to object by motion mobile object or mobile gauge head, the three-dimensional data of obtaining is exactly the data that project the striation on object.The characteristics of this class gauge head are once to obtain the data on laser rays, and normally hundreds of, have higher efficiency, and the minor increment on striation between two points is to be determined by the pixel size along the striation direction.The major defect of this class gauge head is can not the clear edge contour of measuring exactly object, the place that the common corresponding striation in the edge of object disconnects, and this makes this gauge head can't obtain the accurate data of object edge profile.

In addition, traditional bidimensional image measurement is to utilize a ccd video camera to detect the edge contour of object on two dimensional surface, has very high sharpness and precision, at accurate detection field, is widely used.But the method can only detect the edge feature in same plane, can not detect three-dimensional feature.

Summary of the invention

The objective of the invention is to overcome the above-mentioned defect of prior art, a kind of 3-dimensional image measuring method that line-structured light and radiographic measurement are combined has been proposed, the three-dimensional data on the principle quick obtaining body surface of line-structured light can not only be utilized, the accurate edge contour data of space object can also be obtained simultaneously.

The present invention adopts following technical scheme to realize: a kind of 3-dimensional image measuring method based on line-structured light comprises the following steps:

(1) close annular LED light source, open the line-structured light projector, the plane that the line-structured light projector sends and testee intersect a very bright laser striation of generation, video camera is taken the image of this striation, thereby the image of this striation is processed to the center that obtains the laser striation, this center is by O " pixel coordinate of uv coordinate system (u, v) mean;

(2) the closed line structured light projector, open annular LED light source, and video camera obtains the image of testee, and this image is carried out to the sub-pixel edge extraction, obtains the accurate image information of object features;

(3) sub-pixel edge of object in the laser striation center of step (1) and step (2) is intersected and obtains two some P and Q, P point and Q point are both in the laser striation, again on the edge of object, be that P point and Q point are the marginal points on striation, only the point on striation could, by finally being converted to 3 d space coordinate, repeat the two-dimensional image areal coordinate that above-mentioned three steps can obtain obtaining the object edge profile;

(4) demarcate and can obtain the two-dimensional coordinate in optical plane according to the two-dimensional image areal coordinate by line-structured light " intrinsic parameter ", OsXsYs is the two-dimensional coordinate system in optical plane;

(5) demarcate and the two-dimensional coordinate in optical plane can be transformed in the three-dimensional system of coordinate of motion by " the outer parameter " of 3-dimensional image measuring instrument, thereby realize three-dimensional scanning measurement, OmXmYmZm is the three-dimensional system of coordinate of motion.

In the present invention, the extraction at laser striation center adopts gravity model appoach, projects the brightness approximate Gaussian distribution of the laser striation on object, and centre is the brightest, dimmed gradually to both sides, N _i-2to N _i+2location of pixels on striation, V _i-2to V _i+2be the gray-scale value of respective pixel, the gravity model appoach formula is as follows:

$P=\frac{\underset{i=-2}{\overset{i=2}{\mathrm{\Σ}}}{N}_i\×V_i}{\underset{i=-2}{\overset{i=2}{\mathrm{\Σ}}}{V}_i}$

Described image sub-pixel edge extracts the sub-pix algorithm that adopts the poor center of gravity of intensity-based, and the gray-scale value of establishing edge is g _i(i=-3 ,-2 ..., 3), corresponding gray scale difference value is expressed as

$f_i=\frac{g_{i+1}-g_{i-1}}{2}(i=-2,-1,\·\·\·,2)$

Point P (x, y) is the pixel edge point, and some P chooses the neighborhood territory pixel point along direction of scanning, to comprising the pixel that P is ordered, ask respectively gray scale difference f _i(i=-2 ,-1 ..., 2), the place of variation of image grayscale maximum is by f _icenter of gravity about gray scale difference coordinate i means, for left pixel edge point, it is as follows that sub-pixel edge extracts formula:

$\left\{\begin{array}{c}\mathrm{\&delta;}=\frac{{-2f}_{-2}-f_{-1}+f_1+{2f}_2}{f_{-2}+f_{-1}+f_0+{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="HDA00003751576100011.png,HDA00003751576100022.png"\; state="\{\{state\}\}">f</figure-callout>}}_1+f_2}\\ x^{\&prime;}=x+\mathrm{\&delta;}\\ y^{\&prime;}=y\\ \end{array}\right.$

In the present invention in the calibration process of intrinsic parameter, after the two-dimensional image areal coordinate of object edge point is determined, by f (P _r)=P _2dformula obtains the two-dimensional coordinate in optical plane, wherein P _rbe the two-dimensional image areal coordinate of object edge point, f is the corresponding function of this gauge head intrinsic parameter, P _2dit is the two-dimensional coordinate in optical plane after conversion.

The outer parameter of described 3-dimensional image measuring instrument has 6 components, comprise 3 translational components and 3 rotational components, wherein three translational components are the position of 3-dimensional image measuring instrument work origin in world coordinate system, 3 rotational components are three anglecs of rotation of 3-dimensional image measuring instrument two-dimensional coordinate system with respect to world coordinate system, if translational component is M, rotational component is Q, and the three-dimensional coordinate under world coordinate system is P _3d, the three-dimensional coordinate from the optical plane two-dimensional coordinate to world coordinate system is P _3d=QP _2d+ M.

Described 3-dimensional image measuring instrument comprises the line-structured light projector and video camera, wherein the line-structured light projector and video camera are fixed on same horizontal base, the line-structured light projector, video camera are encapsulated in casing together with horizontal base, the angle of the projecting direction of the line-structured light projector and the optical axis direction of video camera is 30 °～35 °, the light hole of the line-structured light projector is between 90mm～100mm to the distance of video camera image plane center, and the front end of camera lens is installed the annular LED light source of being made by LED.

The invention has the beneficial effects as follows: the method can not only be utilized the three-dimensional data on the principle quick obtaining body surface of line-structured light, can also obtain the accurate edge contour data of space object simultaneously; Simultaneously, the method step is simple, and on hardware, only need increase annular LED light source on existing 3-dimensional image measuring instrument can realize.

The accompanying drawing explanation

Fig. 1 is based on the structural representation of the 3-dimensional image measuring instrument of line-structured light;

Fig. 2 is line-structured light inside and outside parameter transformational relation schematic diagram;

Fig. 3 (a) is the crossing image of line-structured light and object;

Fig. 3 (b) is the extraction result at line-structured light striation center;

Fig. 4 is the distribution schematic diagram of laser striation brightness;

Fig. 5 (a) is the testee image;

Fig. 5 (b) is that testee feature sub-pixel edge extracts result;

Fig. 6 is the schematic diagram of gray scale difference gravity model appoach;

Fig. 7 is the crossing structural representation of light strip center of structured light and object edge.

In Fig. 1: 1 video camera; 2 camera lenses; The 3 line-structured light projectors; 4 annular LED light sources.

Embodiment

Below in conjunction with accompanying drawing, the present invention will be further described.

The method of the invention is completed by the 3-dimensional image measuring instrument based on line-structured light.The described 3-dimensional image measuring instrument based on line-structured light comprises the line-structured light projector 3 and video camera 1, and wherein the line-structured light projector 3 and video camera 1 are fixed on same horizontal base, and are encapsulated in casing together with this horizontal base.The angle of the optical axis direction of the projecting direction of the line-structured light projector 3 and video camera 1 is between 30 °～35 °, and the light hole of the line-structured light projector 3 is between 90mm～100mm to the distance of video camera image plane center.In order to realize the radiographic measurement function, at the front end of camera lens, the annular LED light source 4 of being made by red LED is installed.

3-dimensional image measuring method based on line-structured light of the present invention comprises the following steps:

The first step, utilize line-structured light to measure the two-dimensional image areal coordinate that directly by video camera, is obtained the object edge profile, processes the pixel coordinate (u, v) on image planes that obtains the laser striation by image, and as Fig. 2, " uv is image coordinates system to O.Wherein, the two-dimensional image areal coordinate that obtains the object edge profile mainly comprises the following steps:

(1) close annular LED light source 4, open the line-structured light projector 3, the plane that the line-structured light projector 3 sends and testee intersect a very bright laser striation of generation, and video camera 1 is taken the image of this striation, as shown in Fig. 3 (a).Thereby the image of this striation is processed to the center that obtains the laser striation, as shown in Fig. 3 (b), this center is by O, " (u v) means the pixel coordinate of uv coordinate system.In the present invention, the extraction at laser striation center adopts gravity model appoach, projects the brightness approximate Gaussian distribution of the laser striation on object, and centre is the brightest, dimmed gradually to both sides, as shown in Figure 4, and N _i-2to N _i+2location of pixels on striation, V _i-2to V _i+2be the gray-scale value of respective pixel, the gravity model appoach formula is as follows:

$P=\frac{\underset{i=-2}{\overset{i=2}{\mathrm{\&Sigma;}}}{N}_i\&times;V_i}{\underset{i=-2}{\overset{i=2}{\mathrm{\&Sigma;}}}{V}_i}$

(2) the closed line structured light projector 3, open annular LED light source 4, and video camera 1 obtains the image of testee, as shown in Fig. 5 (a), this image is carried out to the sub-pixel edge extraction, obtain the accurate image information of object features, as shown in Fig. 5 (b).In the present invention, the image sub-pixel edge extracts the sub-pix algorithm that adopts the poor center of gravity of intensity-based, and the gray-scale value of establishing edge is g _i(i=-3 ,-2 ..., 3), corresponding gray scale difference value can be expressed as

$f_i=\frac{g_{i+1}-g_{i-1}}{2}(i=-2,-1,\&CenterDot;\&CenterDot;\&CenterDot;,2)$

The edge of image is the place of variation of image grayscale maximum, the pixel edge point is carried out to sub-pixel detection and obtain the position of gray-value variation maximum in fact exactly in the pixel edge neighborhood of a point of trying to achieve, and is corresponding sub-pixel edge point position.Based on above-mentioned analysis, as shown in Figure 6, some P (x, y) is the pixel edge point, some A, and B, C, D is the neighborhood territory pixel point of some P along direction of scanning.Ask respectively gray scale difference f to above-mentioned 5 _i(i=-2 ,-1 ..., 2), the ground of variation of image grayscale maximum can be by f _icenter of gravity about gray scale difference coordinate i means.For left pixel edge point, it is as follows that sub-pixel edge extracts formula:

$\left\{\begin{array}{c}\mathrm{\&delta;}=\frac{{-2f}_{-2}-f_{-1}+f_1+{2f}_2}{f_{-2}+f_{-1}+f_0+{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="HDA00003751576100011.png,HDA00003751576100022.png"\; state="\{\{state\}\}">f</figure-callout>}}_1+f_2}\\ x^{\&prime;}=x+\mathrm{\&delta;}\\ y^{\&prime;}=y\\ \end{array}\right.$

(3) edge of object, generally at laser striation gap, therefore intersects the sub-pixel edge of object in the laser striation center in Fig. 3 (b) and Fig. 5 (b) can obtain two some P and Q, as shown in Figure 7.P point and Q point are both in the laser striation, again on the edge of object.Can obtain the two-dimensional image areal coordinate of object edge point through above three steps.

Second step, demarcate and can obtain the two-dimensional coordinate in optical plane according to the two-dimensional image areal coordinate by line-structured light " intrinsic parameter ", and OsXsYs is the two-dimensional coordinate system in optical plane.

In the present invention, in the calibration process of ability intrinsic parameter, the demarcation of intrinsic parameter is to set up from the CCD image planes to laser beam or the mapping relations of laser plane, and the laser rays on the testee that CCD is received is converted to the two-dimensional coordinate in laser plane.After the two-dimensional image areal coordinate of object edge point is determined, by f (P _r)=P _2dformula obtains the two-dimensional coordinate in optical plane, wherein P _rbe the two-dimensional image areal coordinate of object edge point, f is the corresponding function of this measuring instrument intrinsic parameter, P _2dit is the two-dimensional coordinate in optical plane again after conversion.

The 3rd step, demarcate and the two-dimensional coordinate in optical plane can be transformed in the three-dimensional system of coordinate of motion by " the outer parameter " of 3-dimensional image measuring instrument, thereby realize three-dimensional scanning measurement, and OmXmYmZm is the three-dimensional system of coordinate of motion.

The outer parameter of 3-dimensional image measuring instrument has 6 components, 3 translational components, the i.e. position of 3-dimensional image measuring instrument work origin in world coordinate system; 3 rotational components, gauge head one dimension or two-dimensional coordinate system are with respect to three anglecs of rotation of world coordinate system.If translational component is M, rotational component is Q, and the three-dimensional coordinate under world coordinate system is P _3d, the three-dimensional coordinate from 3-dimensional image measuring instrument two-dimensional coordinate to world coordinate system is P _3d=QP _2d+ M.

Get final product the three-dimensional data on the quick obtaining body surface by above-mentioned steps, can also obtain the accurate edge contour data of space object simultaneously.

Claims (6)

1. the 3-dimensional image measuring method based on line-structured light is characterized in that comprising the following steps:

(1) close annular LED light source (4), open the line-structured light projector (3), the plane that the line-structured light projector (3) sends and testee intersect a laser striation of generation, video camera (1) is taken the image of this striation, thereby the image of this striation is processed to the center that obtains the laser striation, this center is by O " pixel coordinate of uv coordinate system (u, v) mean;

(2) closed line structured light projector (3), open annular LED light source (4), and video camera (1) obtains the image of testee, and this image is carried out to the sub-pixel edge extraction, obtains the accurate image information of object features;

(3) sub-pixel edge of object in the laser striation center of step (1) and step (2) is intersected and obtains two some P and Q, P point and Q point are both in the laser striation, again on the edge of object, that is to say that P point and Q point are the marginal points on striation, repeat the two-dimensional image areal coordinate that above-mentioned three steps can obtain obtaining the object edge profile;

(4) demarcate and can obtain the two-dimensional coordinate in optical plane according to the two-dimensional image areal coordinate by the line-structured light intrinsic parameter, OsXsYs is the two-dimensional coordinate system in optical plane;

(5) external parameters calibration by the 3-dimensional image measuring instrument can be transformed into the two-dimensional coordinate in optical plane in the three-dimensional system of coordinate of motion, thereby realizes three-dimensional scanning measurement, and OmXmYmZm is the three-dimensional system of coordinate of motion.

2. the 3-dimensional image measuring method based on line-structured light according to claim 1, it is characterized in that: the extraction at described laser striation center adopts gravity model appoach, projects the brightness approximate Gaussian distribution of the laser striation on object, and centre is the brightest, dimmed gradually to both sides, N _i-2to N _i+2location of pixels on striation, V _i-2to V _i+2be the gray-scale value of respective pixel, the gravity model appoach formula is as follows: $P=\frac{\underset{i=-2}{\overset{i=2}{\mathrm{\&Sigma;}}}{N}_i\&times;V_i}{\underset{i=-2}{\overset{i=2}{\mathrm{\&Sigma;}}}{V}_i}$

3. the 3-dimensional image measuring method based on line-structured light according to claim 1 is characterized in that: described image sub-pixel edge extracts the sub-pix algorithm that adopts the poor center of gravity of intensity-based, and the gray-scale value of establishing edge is g _i(i=-3 ,-2 ..., 3), corresponding gray scale difference value is expressed as:

$f_i=\frac{g_{i+1}-g_{i-1}}{2}(i=-2,-1,\&CenterDot;\&CenterDot;\&CenterDot;,2)$

Point P (x, y) is the pixel edge point, and some P chooses the neighborhood territory pixel point along direction of scanning, to comprising the pixel that P is ordered, ask respectively gray scale difference f _i(i=-2 ,-1 ..., 2), the place of variation of image grayscale maximum is by f _icenter of gravity about gray scale difference coordinate i means, for left pixel edge point, it is as follows that sub-pixel edge extracts formula:

$\left\{\begin{array}{c}\mathrm{\&delta;}=\frac{{-2f}_{-2}-f_{-1}+f_1+{2f}_2}{f_{-2}+f_{-1}+f_0+f_1+f_2}\\ x^{\&prime;}=x+\mathrm{\&delta;}\\ y^{\&prime;}=y\\ \end{array}\right.$

4. the 3-dimensional image measuring method based on line-structured light according to claim 1, is characterized in that: in the calibration process of described intrinsic parameter, after the two-dimensional image areal coordinate of object edge point is determined, by f (P _r)=P _2dformula obtains the two-dimensional coordinate in optical plane, wherein P _rbe the two-dimensional image areal coordinate of object edge point, f is the corresponding function of this measuring instrument intrinsic parameter, P _2dit is the two-dimensional coordinate in optical plane again after conversion.

5. the 3-dimensional image measuring method based on line-structured light according to claim 1, it is characterized in that: the outer parameter of described 3-dimensional image measuring instrument has 6 components, comprise 3 translational components and 3 rotational components, wherein three translational components are the position of 3-dimensional image measuring instrument work origin in world coordinate system, 3 rotational components are 3-dimensional image measuring instrument one dimension or two-dimensional coordinate system three anglecs of rotation with respect to world coordinate system, if translational component is M, rotational component is Q, and the three-dimensional coordinate under world coordinate system is P _3d, the three-dimensional coordinate from the optical plane two-dimensional coordinate to world coordinate system is P _3d=QP _2d+ M.

6. the 3-dimensional image measuring method based on line-structured light according to claim 1 or 5, it is characterized in that: described 3-dimensional image measuring instrument comprises the line-structured light projector (3) and video camera (1), the line-structured light projector (3) and video camera (1) are fixed on same horizontal base, the line-structured light projector (3), video camera (1) is encapsulated in casing together with horizontal base, the angle of the optical axis direction of the projecting direction of the line-structured light projector (3) and video camera (1) is 30 °～35 °, the light hole of the line-structured light projector (3) is between 90mm～100mm to the distance of video camera image plane center, the front end of camera lens is installed the annular LED light source (4) of being made by LED.

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